Population is your number one moral problem. Too many people = low to 0 pop. In my games, most of my worlds in GalCiv end up building a colony ship, sticking most of the population on it, and launching it into space. I just build a super large stack of these excess wastage of people. Other players "sell" them to the aliens.

To figure out what is the proper levels of taxing, at the start of the game, I set my tax rate equal to what gives my homeworld 100% morale. And leave it there, for most of the game.

That's it. Improve a worlds PQ as much as possible, and ship off vast majority of the game. It sucks from consistancy point of view, but it is how the game is designed.

And remember, in GalCiv, for planets, don't build everything on the shopping list of what's available. Only build what you need. Most worlds will never see the benefits of most items.